1. Field of the Invention
The present invention relates to a flyback transformer and, more particularly, to an element installation arrangement for installing an element, such as a diode, used therein.
2. Description of the Prior Art
The flyback transformer is used, for example, in a television receiver or CRT display apparatus for supplying a high DC voltage to a cathode ray tube for the acceleration of the electron beam and, for this purpose, a number of diodes are provided in the flyback transformer so as to rectify the output voltage of the secondary windings.
An example of a prior art flyback transformer is shown in FIG. 1, which comprises inner bobbin 3 and outer bobbin 11. Inner bobbin 3 is integrally formed with a base portion 2 mounted with a plurality of pins 1. Primary winding 4 and tertiary winding 5 are wound on inner bobbin 3. Outer bobbin 11 has a plurality of flanges defining a coil groove 9 and a separation groove 10. A secondary winding 12, which is divided into a plurality of sections 12a, is wound on outer bobbin 11 such that each coil section is wound in coil groove 9. The coil sections are connected in series through diodes 15, each supported by an installation arrangement defined by a pair of holders 26 and 27 provided in separation groove 10.
Inner bobbin 3 is inserted into outer bobbin 11 and both bobbins are accommodated in a casing 16 made of electric insulation material, such as synthetic resin. After locating the bobbins inside casing 16, molten synthetic resin (not shown) is filled in, which becomes hard in a short period of time. Thereafter, a pair of U-shaped ferrite cores 17 and 18 are mounted to define an O-shaped core unit such that a portion of the O-shaped core unit extends through inner bobbin 3. The O-shaped core unit is provided for forming a magnetic circuit for the magnetic flux generated by the windings.
An equivalent circuit of the flyback transformer is shown in FIG. 2 which clearly shows that secondary winding 12 is defined by the serial connection of coil sections 12a through diodes 15. One end of secondary winding 12 is grounded through a pin 21 and the other end thereof is connected through a diode to a line 22 which will carry a high voltage.
According to the prior art flyback transformer, such as disclosed in Japanese Utility Model Laid-open Publication No. 118024/1978 entitled "Flyback Transformer" and issued Sept. 20, 1978, each diode 15 is supported by a pair of holders 26 and 27, such as shown in FIG. 3. Holders 26 and 27 are located on outer bobbin 11, and they extend from the bottom of separation groove 10. A distance between a pair of holders 26 and 27 is a little longer than the length of diode 15 measured in the axial direction. Holders 26 and 27 have grooves 26a and 27a, respectively, at their ends remote from the ends connected to the bottom of separation groove 10. The width of each of grooves 26a and 27a is slightly narrower than the diameter of lead wire 15a or 15b extending in opposite directions from the body of diode 15. Accordingly, the diode 15 is supported such that lead wires 15a and 15b are pressure fitted in grooves 26a and 27a, respectively.
In this case, a problem arises when mounting the diodes on holders 26 and 27 such that a pushing force applied to the diode may result in an undesirable bending of lead wires 15a and 15b at the neck thereof where it is connected to the body of the diode. Since the holders support not the diode body itself, but the lead wires extending from the diode body, a diode with such a bent lead wire may be mounted in an offset position between holders 26 and 27. For example, the diode body may be raised above the holder, or it may be pushed down close to the bottom of separation goove 10, as indicated by a broken line in FIG. 4. When this happens, a space between the diode body and the wall of the casing, or a space between the diode body and the bottom of separation groove 10, becomes very narrow. Thus, when the molten resin is injected, it can not flow through such a narrow space, resulting in undesirable air bubbles around the diode body. Thus, the insulation breakdown of the diode becomes poor.
To eliminate such a disadvantage, each of the diodes must be checked after it is mounted on a pair of holders.
Furthermore, as shown in FIG. 4, according to the prior art flyback transformer, the distance L1 between holders 26 and 27 is made slightly longer than the length K of the diode body so as to facilitate the mounting of each diode between holders 26 and 27. Furthermore, the thickness T of each holder is made comparatively thick so as to ensure the rigid support of diode 15 between holders 26 and 27. Accordingly the total distance L2 occupied by a pair of holders 26 and 27 is relatively large, resulting in the large size of outer bobbin, and in turn, the large size of flyback transformer.